Not Applicable
1. Field of the Invention
The present invention relates to the field of self adjusting tools and specifically to locking pliers, wrenches, or vises which self adjust to the size of the work piece.
2. Background Information
Locking pliers are well known in the industry and are exemplified by the Vise Grip(copyright) line of pliers. This type of tool offers significant advantage over conventional pliers in that it can be locked on to a work piece by squeezing the handles together until they over-center slightly, locking in position, the plier and work piece can then be manipulated without exerting any additional effort to keep the pliers closed. An adjustment screw adjusts the plier to fit a range of work piece sizes.
One major disadvantage to known locking pliers it that the adjusting screw, while effective, is slow to manipulate. The full range of adjustment may be as much as one inch or more and requires many turns of the adjusting screw to accomplish. The time required to perform this operation can be frustrating to the user. In addition, it is nearly impossible to make this adjustment one handed, requiring one hand to hold the plier while the other turns the adjusting screw.
A plier which automatically adjusts to the size of the work piece would be significantly more convenient to use. Such pliers exist, but typically have their own drawbacks. One such is the Sears Autolock Plier, marketed by Sears, Roebuck, and Co., and described in U.S. Pat. No. 3,600,986. In this plier, the adjusting knob for varying the grip force is positioned in the center of the tool, between the handles. This location is difficult to access, the knob is relatively small, and turns in the opposite direction from what would be expected. The result is a plier which provides less than satisfactory performance.
There is a need for a locking plier which self adjusts to the size of the work piece. The grip force should be easily and conveniently adjustable by the user, preferably in a conventional manner and location. Ideally, the adjustment would be located at the rear of the plier, readily accessible to the user.
The present invention is directed to an apparatus for providing a self adjusting closure mechanism for a locking plier or similar device. Central to the invention are a set of one or more friction pawls which slide along a support rod, moved by a push link working against a spring. The push link is free to rotate between two positions relative to the rod, as it slides. In the first position, and in between, the push link bears against the center of the friction pawls and they remain free to slide along the rod. When the push link rotates to the second position, it presses on the edge of the pawls, causing them to tilt, coupling to the rod and preventing movement along the rod. In a typical locking plier, the support rod is mounted to the frame and the opposite end of the push link connects to the handle. As the handle closes, the push link rotates towards its second position and optionally slides along the support rod. When the friction pawls lock, the plier begins to grip and lock on to the work piece.
According to an aspect of the invention there is provided a means of adjusting the relative angle of the second position of the push link when the pawls lock. Preferably this is in the form of a circular wedge, or helix which fits in between the push link and the pawls. Ideally, this helix is coupled to the support rod so that it slides along with the push link and pawls, but rotates along with the support rod, independently of the link and pawls. This allows the grip force of the locking plier to be adjusted by rotating the support rod. Preferably, an adjusting knob, connected to the support rod extends to the rear of the plier for easy access.
Normally, the friction pawls will unlock from the support rod when released by the push link, with the assistance of the spring. According to another aspect of the invention the push link may incorporate a contact point on the side opposite from that which locks the pawls to positively unlock the pawls by tilting them back to their unlocked position.
Further in accordance with the invention the force applied by the spring to the friction pawls may be adjustable. This provides a means of varying the normal position of the push link and pawls along the length of the support rod. In turn, this varies the width of the plier jaws in their normal, open position.
The advantages of such an apparatus are a self adjusting mechanism which automatically locks at a repeatable angle between the push link and rod. When used with a typical locking plier, this translates to the handle always locking at the same relative position. The plier self adjusts to the size of the work piece because when the jaws contact the work piece, the push link slides along the support rod until the angular position where the pawls lock to the rod is reached. The distance the push link moves along the rod varies with the size of the work piece, but the angle of the push link, and the handle, when the pawls lock, is substantially always the same. The adjustment varies this angle slightly allowing the grip force of the plier to be adjusted by the user.